Light-emitting diodes (LEDs) can be used in many applications such as general lighting. LEDs offer several advantages over traditional light sources such as fluorescent lamps and incandescent lamps. For example, LEDs have significant lower power consumption. Unlike traditional light sources such as incandescent light bulbs that convert significant electrical current heating up the metal filaments to a temperature high enough to generate light, LEDs generate virtually no heat and utilize a fraction of the energy to produce an equivalent lumen of lighting. For example, in a light bulb application, an LED light source may consume less than 7 Watts to produce the same amount of brightness compared to an incandescent light source consuming approximately 60 Watts.
Furthermore, the operational life of an LED can be extended to over 50,000 hours which is significantly longer than the average life of an incandescent bulb, e.g., 5000 hours, and the average life of a fluorescent lamp, e.g., 15,000 hours. Moreover, LEDs contain no mercury or any other hazardous materials or chemicals and emit zero ultra violet (UV) radiation unlike incandescent or fluorescent lamps. The use of the LEDs materially enhances the environment and conserves energy.
Traditionally, an AC/DC converter converts an AC voltage to a substantial DC voltage to power the LEDs. FIG. 1 illustrates a typical driving circuit 100 for driving a light source, e.g., an LED array 108. The driving circuit 100 includes a bridge rectifier 104 for rectifying the AC voltage to a rectified AC voltage, and an electrolytic capacitor Cbulk having a relatively large size coupled to the bridge rectifier 104 for filtering the rectified AC voltage to provide a substantially constant DC voltage VIN.
The driving circuit 100 further includes a switching-mode DC/DC converter 122 that converts the DC voltage VIN to a DC voltage VOUT across a capacitor 116 to power the LED array 108. In operation, a controller 118 generates an ON/OFF signal to turn a switch 106 fully on and off alternately to control the power for the LED array 108. However, the turn-on and turn-off of the switch 106 generates electromagnetic interference (EMI) noise such that an EMI filter 130 is required to suppress the noise on the power line. In addition, the switching-mode DC/DC converter 122 usually includes elements such as an inductor 112 and a capacitor 116 for energy storage and/or filtering function. Such elements are also relatively large in size and are difficult to be placed into the commercial available lighting fixtures such as E12, E14, E17 LED bulbs or T-5 and T-8 LED light tubes.